Piggyback: How big is too big?

[SteveL]

I know piggybacking is all about the balance, and not really about the weight, but just how big is too big? I have a NexStar 8 GPS on a wedge, and am looking at sticking a second OTA on the top in the near future (along with a counterweight bar along the bottom) for wide field work and autoguiding. I`m looking at an ED80 but wondering if thats too big and I should look at a 66mm OTA instead. Aperture rules, but balance is eveything when guiding.

Any advice would be gratefully received.

[centroid]

Weight is a significant consideration Steve, as although it might be balanced about each axis, the total weight is still the 'load' that is placed upon the 'mount' itself.

I have an ED80 'piggy backed' on my 10" LX200GPS, plus 7kg of balance weigths. In addition to this, when the SXVF-H9C and DSI (guide cam), plus other 'bits & bobs', the mount is subject to quite a significant 'load'.

I did look at also 'piggybacking' the PST, but decided that it might be 'the straw to break the camels back', so didn't 'chance it'.

A 66mm scope, would make a reasonable 'guide scope', but finding a suitable 'guide star', in some areas of the sky, would be more difficult than with an 80mm, a 90mm scope, and so on.

My 'gut feeling', is that an ED80, would be a little too heavy/large, to mount on an 8" SCT. However, someone may well say that they are doing this without any problems.

Dave

[barkis]

Steve, I have a LX90 12", and like you, I was contemplating putting my ED80 on as an imaging scope, with the necessary balancing gear to counteract the weight on top. I made enquiries via Telescope Service, as to a suitable rig for doing the job. The chap emailed me, and advised me against doing it, for precisely the same reason as Dave has just given.

I guess the TS guy deserves a pat on the back, as he put his professionalism before a potential sale.

I did a post on this at the time, and most agreed, including Steve (Flo), all agreeing the extra weight would eventually put strain on the gears and motors.

Ron.

[SteveL]

OK, so thats two "NO" votes

So, a 66mm about right then? Suggestions for a suitable guide scope? (These look super sexy)

[Greg]

Doesn't MartinB have that set up??

Greg

[GazOC]

The LX motors arn't the same standard as the Celestrons.

[daz]

I've seen the Equinox in the flesh and sexy IS the word! I think you'd be fine with that Steve

[Greg]

Gaz,

I'm responding to SteveL's original post :?

I have a NexStar 8 GPS on a wedge, and am looking at sticking a second OTA on the top in the near future (along with a counterweight bar along the bottom)

Not about barkis's LX90 :?

Or am I getting it wrong here??

Wouldn't be the first time ..

[Nessy]

Hi Steve, apart from the wedge-self-build I am attempting...I was planning on making some purchases this week. Originally I was going for the Guide-scope but ater seeing your success with the OAG I thought of perhaps going this route. However, seeing your now looking at doing an about turn I was wondering why (i.e. have you found problems etc.) or are you just 'adding'?

Ta again!

[Helen]

I think, looking at Martin's picture, that the scope on top is an ST80 not an ED80. I've just acquired an ST80 and it is very light (I'd say lighter than my WO ZS66) because there is more plastic and less metal...

Can't help on the balance point Steve, not reached that point yet, but very interested in the replies for when I do!

Helen

[Greg]

I think, looking at Martin's picture, that the scope on top is an ST80 not an ED80.

It's an ED80 Helen....

I have the Pro version..It's in Champagne 8) ....

[SteveL]

partially just equipment aquisition but also gives me some flexibility. A second OTA will allow me:

- autoguiding with second scope

- wide field imaging the second scope (and then autoguiding on the NS8GPS)

- and its an excuse to get the counterbalance kit

The OAG works great, but I would imagine that finding a guide star might be a problem in certain shots.

I`ll wait and see what MartinB says when he returns.

[Helen]

I think, looking at Martin's picture, that the scope on top is an ST80 not an ED80.

It's an ED80 Helen....

I have the Pro version..It's in Champagne 8) ....

Happy to be corrected Greg looking again, it does look better made than mine!

Helen

[centroid]

The LX motors arn't the same standard as the Celestrons.

The motors on my 10" LX are now 5.5 years old, and have been well used during that time.

I've had a guide scope 'piggybacked' on the LX for most all of that time. An ED 80 for the past 18 months or so, and an ST80 prior to that. A 3D counter-balance 'rail system' has been has been in-place throughout. I had to increase the counter-balance weight by about 3kg, when I installed the ED80.

Either I've been lucky, or the LX motors are as good as any.

Dave

[Nessy]

ok....I had a hunch it was for those purposes but just wanted to check there were no probs!

I think I will still go and try the OAG then as its the cheapest way to go currently.....

Long term I think ED80 on a CPC11

[GazOC]

The LX motors arn't the same standard as the Celestrons.

The motors on my 10" LX are now 5.5 years old, and have been well used during that time.

I've had a guide scope 'piggybacked' on the LX for most all of that time. An ED 80 for the past 18 months or so, and an ST80 prior to that. A 3D counter-balance 'rail system' has been has been in-place throughout. I had to increase the counter-balance weight by about 3kg, when I installed the ED80.

Either I've been lucky, or the LX motors are as good as any.

Dave

I stand to be corrected but I thought the LX90 gears etc are the plastic type whereas the Celestron are nearer the LX200 specs?

Might be wrong though...

[themos]

I'm trying to think what the requirements are for a guiding device and

• 
  [li]chromatic aberration - don't care - use a filter[/li]
  [li]field curvature - don't care - only need to focus one star[/li]
  [li]baffles etc - don't care - contrast should be adequate without[/li]
  [li]secondary - not needed[/li]
  

Basically, a magnifying glass on a swivel joint and a CCD should do it, a frame for placing the CCD in 3d position and attitude being the critical factor. but that's just mad.

Isn't it?

[centroid]

The LX motors arn't the same standard as the Celestrons.

The motors on my 10" LX are now 5.5 years old, and have been well used during that time.

I've had a guide scope 'piggybacked' on the LX for most all of that time. An ED 80 for the past 18 months or so, and an ST80 prior to that. A 3D counter-balance 'rail system' has been has been in-place throughout. I had to increase the counter-balance weight by about 3kg, when I installed the ED80.

Either I've been lucky, or the LX motors are as good as any.

Dave

I stand to be corrected but I thought the LX90 gears etc are the plastic type whereas the Celestron are nearer the LX200 specs?

Might be wrong though...

Hmmm, you've got me thinking now, but I assumed that the LX0 gears where the same as those on my LX200GPS. On the LX200GPS, the small 'transfer gears' are made of Nylon/Plastic, but the large cog-wheel and worm gear that drives it, are metal.

Last winter, I changed the plastic 'transfer gears' for a set of s/steel 'Bucks Gears'. Not because the original Plastic one's were worn, as they were still in excellent order, but to improve the Periodic Error performance of the mount.

However, having spent £90 on these 'Bucks gears', I found that they performed no differently to the original platic Meade gears. What did make the difference was the recommended changes to make the 'worm gear' mesh tighter with the large cog-wheel. This comprised a small brass bush and a rubber 'O' ring, for which in reallity, I'd paid £90 for

I believe that the current generation of LX200s, now have brass transfer gears.

Dave

[GazOC]

I really don't know the current 'state of play' Dave but when I owned a 8" LX90 3 or so years ago I was told that I shouldn't try to piggyback the same gear that I'd seen piggybacked on 8" LX200s because the gears on the LX90 were inferior. I think I got the info from the Meade LX Yahoo Group and they were usually pretty spot on with their advice but thats 3 year old information and secondhand at that so I've no way of knowing how accurate it is. It just seemed make sense to me when you consider that you have to make some sacrifices to get the same OTA as the LX200 but at such a reduced price?